MBMS (Multimedia Broadcast Multicast Service) is used to provide multimedia broadcast and multicast services for users in a wireless cell. In an LTE (Long Term Evolution) system, it can be provided on a frequency layer dedicated to MBMS or the one shared with MBMS.
An LTE cell supporting MBMS can be an MBMS dedicated cell or an MBMS/unicast mixed cell. MBMS service can perform single-cell transmission or multi-cell transmission. The multi-cell transmission of MBMS needs to support an MBSFN (Multicast/Broadcast over Single-Frequency Network) transmission mode.
MBSFN means synchronous transmission in a plurality of cells at the same frequency and time. The use of this transmission mode can save frequency resources and improve the availability of frequency spectrum. This technology requires a plurality of cells to send the identical contents at the same time. In this way, a UE (User Equipment) receiver takes a plurality of MBSFN cells as a big cell. Therefore, a terminal will not suffer the inter-cell interference transmitted by an adjacent cell and will benefit from the superposition of signals from a plurality of MBSFN cells. Both an MBMS dedicated cell and an MBMS/unicast mixed cell can adopt the MBSFN transmission mode. Besides, the use of advanced terminal receivers can solve the problem of time difference of multipath propagation, thus eliminating the intra-cell interference. Diversity effects brought by this multi-cell co-frequency transmission can also solve the problem of dead zone coverage, enhance the reliability of reception and improve the coverage rate.
MBMS multi-cell transmission technology has the following technical features:
(1) Synchronously transmit MBMS in an MBSFN area.
(2) Support the merging of multi-cell MBMS transmission.
(3) Map an MTCH (Multicast Traffic Channel) and an MCCH (Multicast Control Channel) to an MCH (Multicast Channel) for PTM (Point To Multipoint) transmission.
(4) Configure an MBSFN synchronization area in a semi-static state, for example, through O&M (Operation and Maintenance).
Logic channels relating to MBMS transmission mainly include BCCH (Broadcast Control Channel), MCCH and MTCH. The major functions of each channel are as follows:
(1) A BCCH is used for a network to broadcast the system information to a terminal.
For MBMS, a BCCH carries the configuration information of an MCCH, such as repetition period of the MCCH, initial radio frame offset, subframe position, MCCH modification period, indication mode of MCCH modification notices, MCS (Modulation Coding Scheme) format for MCCH transmission, etc., so that a terminal can find the resource position of the MCCH and the BCCH does not carry the specific information about MBMS service.
(2) An MCCH is a PTM downlink channel and is used for a network to transmit the MBMS-related control information in the MBSFN area to a terminal.
An MCCH correspond to one or a plurality of MTCHs, that is to say, it can carry the control information about plurality of MTCHs. The information contained in an MCCH includes subframe distribution and subframe distribution repetition period of the MBSFN area, and configuration information of a PMCH (Physical Multicast Channel) or an MCH, for example: MBMS session information, data MCS format configuration, PMCH subframe position, scheduling period, etc.
(3) An MTCH is a PTM downlink channel and is used for a network to send the specific MBMS service data to a terminal.
The network indicates configuration information about an MCCH using a BCCH to the terminal and provides (P) MCH information using an MCCH for the terminal, so that the terminal reads the MSI about specific services on (P) MCH, thus receiving MBMS service on an MTCH.
A schematic diagram of the relation between an MBMS service area and an MBSFN synchronization area in the prior art is shown in FIG. 1.
The MBMS service area is comprised of one or a plurality of identifications, each of which is mapped to one or a plurality of cells. It is carried by a in a BM-SC (Broadcast Multicast Service Center) session message to a base station.
An MBSFN area is comprised of a group of cells in a synchronization area. These cells send the MBSFN synchronously. The MBSFN area is planned by an MCE (MBMS Coordinating entity) according to the operator's strategy and informed in an M2 interface message to a base station.
An MBSFN area reserved cell is also a synchronization area where an MBSFN is not sent.
Now, the available LTE MBMS logical architecture is shown in FIG. 2, wherein, an MCE is the centralized node at RAN side, while the interface M2 is the logic interface between an MCE and an eNB (evolved Node B) and can be used for transmitting the area identifications of an MBSFN. The scheduling information of an MCE to MBMS service is used for updating MCCH configuration, forwarding session start, closure and update messages from an MME, and managing and configuring the interface M2.
In the prior art, before MBMS transmission, an MCE needs to count the number of UE which is interested in MBMS service in an area and to allocate the resources subsequently according to statistical results. As shown in FIG. 3, an MCE is responsible for the allocation of MBSFN resources and corresponding configuration. So the receiving state of UE to a certain MBMS service should be fed back to the MCE which will adjust an MBSFN area in a dynamic or semi-static state according to the information, thus ensuring the effective use of resources.
Therein, details of an MCE sending a counting request to an eNB have not been determined, while the counting request sent by the eNB to UE is carried in an MCCH. Here the counting request is an MBMS receiving state reporting request and counting response means MBMS receiving state reporting.
In the procedure of realizing the objects of the present invention, at least the following problems existing in the current technologies were found:
In an LTE system, the counting request sent by an eNB to UE is carried in an MCCH. Therefore, different cells in an MBSFN area must be transmitted synchronously to ensure synchronous transmission characteristics of an MCCH. Although a mechanism of an MCE informing an eNB to count UE MBMS service receiving states is supported now, it fails to ensure the synchronous transmission of the information in an MCCH.